Hello folks!

I have a 1996 Tahoe with a 5.7 vortech, 4L60E 4 speed tranny, B&M Megashifter. Every thing is pretty much stock. All replacement parts are GM. I have been battling some kind of misfiring issue and so far it's beating me. This is what I have done so far. New iridium plugs, new spark plug wires, new distributor cap, brand new injectors, newly serviced K&N filter, have had intake nd vac lines checked for leaks. If he Tahoe is idling it is smooth as silk. Increasing the rpm's while in park there is no noticeable misfiring going on. So I engage the mega shifter and drop it down into 1 and take off at a reasonable rate of speed. If I am light on the pedal it gets up around 2500 and its spitting, hicupping, and crapping out. Id I put the pedal down and take it up to around 4k it seems to kick ***. BTW, this did this before I installed the megashifter. This does this in all gears. Some folks have suggested new fuel pump, cam issues, replace distributor, upgraded valve body in the tranny etc etc Some one out there has to have had a similar issue or maybe even has fixed the issue. I don't want to whine but I an throwing cash into this car by the truck load and it is driving me crazy. As long as I am into the pedal it has a ton of power and runs like a beast considering its 90% stock.

I am not a skilled mechanic. My mechanic connected his snap on diag unit and we went for a cruise and he was studying the engine while I was driving. Nothing super crazy. It looked like plug # 8 was misfiring bad. He thought it might be a cracked plug so we replaced it. We could not see evidence of any cracking but it did lower the number of misfires.

Anyway if anyone can help I would greatly appreciate it.

 

Welcome to the forum. Not sure what a Megashifter is but the first thing I would check is the fuel pressure. Does your model year specify iridium spark plugs? If not, you might put in the specified plugs.

 

Thanks

I have been told to check that on the fuel pressure. If it was the pressure wouldn't affect it all of the time? We took the Tahoe out last night. The megashifter allows you to wind out the gears of your auto trans. Its kind of like being able to decide what your shift points are going to be. The Megashifter is made by B&M performance. I have only had it for a week so my explanation night be weak. The important thing is that the problem was there before the shifter. The Tahoe runs it just has this annoying misfiring that happens in all gears and it seems to be in the range of 2.5k rpms.